In vfl3, steric interactions between nearby flagella (e.g. Fig. REF A)
can lead to intermittent beating and reduction in beat frequency.
Even when measured beat frequencies differ for flagella on the same cell, periods of phase-locking are observed,
which we attribute to hydrodynamic interactions [1]}, [2]}, [3]} (see also SI Video 1).
In the tri-flagellates of Figs. REF D&E, beating of a given flagella pair becomes strongly coupled,
with IP or respectively AP synchrony being preferred when flagella are oriented with power strokes parallel or respectively anti-parallel
(compare \(f_0\) ,\(f_2\)  in D with \(f_0\) ,\(f_2\)  in E).
Even biflagellate vfl3 cells with a native CR-like configuration cannot perform IP breaststrokes (e.g. Fig REF B).
In contrast wildtype CR flagella operating over a large frequency range are able achieve robust synchrony,
despite intrinsic cis/trans frequency differences of up to \(30\%\)  during slips,
or conditions of physiological stress such as deflagellation [4]}.
Thus possession of functional or complete DFs appears necessary for CR flagellar synchrony.
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